The process capability index, also known as the process capability ratio. It is the ability of a process to produce output within specification limits, which is referred as Cp (Potential) and Cpk (Capability Index). Given here is the process capability index formula to find the potential of a process, which is the process capability index. This Cp and Cpk formula uses the Upper and lower specification limits and the standard deviation to find the Process Capability ratio.

Where,

USL = Upper Specification Limit,

LSL = Lower Specification Limit.

A data set has USL of 7, LSL of 9, Standard deviation of 14 and Mean of 6. Substituiting the values in the above given Cp and Cpk Formula, you will get the Process Capability Index values Cp as -0.024 and Cpk as -0.071.